1. Field of the Invention
The present invention relates to a camera shutter release control and automatic film sensitivity setting, and more particularly, such a camera which carries out an exposure operation at a predetermined fast shutter speed until it is transferred to a normal photographing condition, that is, until a film loaded in the camera is wound up to a position where a film counter indicates the frame number "1".
2. Description of Prior Arts
A camera of this type which sequentially carries out an exposure operation at a predetermined fast shutter speed until transfer to a normal photographing condition is known by Japanese Patent Laid-open Publication No. 125030/1983. The camera of this type is advantageous since it can be transferred to the normal photographing condition quickly.
On the other hand, a shutter release operation is inhibited in some cameras under a bad-exposure condition. For example, there are cameras which inhibit a release operation until a proper focus condition is achieved by automatic focusing and also cameras which inhibit a release operation until an electronic flash device becomes ready for flashing. It is the concept of these cameras that a release operation should be inhibited until achievement of a proper photographing condition.
However, if such a concept is used for the camera of the type disclosed in the Japanese publication, shutter release operation is inhibited if a proper photographing condition is not achieved even before transfer to the normal photographing condition i.e., before the film is advanced to the first frame. If the camera is constructed in a conventional manner to allow a film winding-up operation only after completion of an exposure operation started by a shutter release operation, the inhibition of a release operation also leads to inhibition of a film winding-up operation, so that the camera cannot be transferred to the normal photographing condition until achievement of a proper photographing condition. Accordingly, it takes a long time for the camera to be transferred to the normal photographing condition, and sometimes a shooting chance is missed.
By the way, a film cartridge having a code pattern on its outer circumference is available recently in the market. The code pattern represents the film sensitivity (hereinafter referred to as ISO) of the film contained in the cartridge. The code pattern makes it possible for a camera to automatically set the ISO value of the film being used. Such cameras capable of reading the code pattern for automatic setting of the ISO value of the film being used are disclosed in U.S. patent Nos. 4,431,283 and 4,200,371. The code pattern may be read at various times, for example, (i) during each exposure operation, (ii) upon loading of a film cartridge into a camera, and (iii) upon closure of a rear cover of a camera. Here, (ii) and (iii) are the cameras disclosed in U.S. patent Nos. 4,200,371 and 4,431,283, respectively.
If the cited camera of the type known by the Japanese publication No. 125030/1983 is constructed to read the code pattern for automatic setting of the ISO value of the film being used, it becomes more convenient to a camera operator. However, if the code pattern is read at any of the times (i), (ii) or (iii) mentioned above, the camera will suffer from the following disadvantages:
(a) In (i), the number of the reading operators increases, resulting in much consumption of electric power. This disadvantage becomes more serious if the camera is constructed to automatically wind-up and rewind a film by using an electric motor, as many recent cameras are. PA1 (b) In the case of the (ii) or (iii), consumption of electric power is not a problem since the reading of the code pattern is effected only once per film cartridge. However, the camera must have either a detection member for detecting the loading of a film cartridge or a detection member for detecting the closure of the rear cover of the camera. As the camera is already necessarily provided with a detection member that changes from a first state to a second state upon transfer of the camera to the normal photographing condition, addition of an extra detection switch as described above makes it difficult to produce the camera at a low cost as well as to design the same to be light and compact.
The camera constructed to read the code pattern for automatic ISO-value setting should also allow manual ISO-value setting for accommodation to a film cartridge with no code pattern. In the case where the automatically set ISO value or the manually set ISO value is stored in an electric storage means, the ISO value stored in the storage means is erased when an old battery of the camera is replaced with a new one, causing the problem that the camera may be unable to effect correct exposure control and the camera operator can not recognize it. Such a problem will occur particularly when the battery replacement is carried out while the camera is in the normal photographing condition, that is, in case some frames of the film are left unexposed. Use of a back-up battery or a back-up capacitor is one method to solve the problem. But this method makes it necessary to provide the camera with a special chamber to receive the back-up battery or the back-up capacitor causing the new problem that the camera becomes bulky.